Coating compositions with anticorrosion properties

ABSTRACT

Anticorrosive coating compositions as disclosed comprise a binding polymer and an aluminum phosphate corrosion inhibiting pigment dispersed therein. The coating composition comprises up to 25 percent by weight aluminum phosphate. The binding polymer can include solvent-borne polymers, water-borne polymers, solventless polymers, and combinations thereof. The aluminum phosphate is made by sol gel process of combining an aluminum salt with phosphoric acid and a base material. Aluminum phosphate colloidal particles are nanometer sized, and aggregate to form substantially spherical particles. The coating composition provides a controlled delivery of phosphate anions of 100 to 1,500 ppm, depending on post-formation treatment of the aluminum phosphate, and has a total solubles content of less than 1500 ppm, The amorphous aluminum phosphate is free of alkali metals and alkaline earth metals, and has a water adsorption potential of up to about 25 percent by weight water when present in a cured film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.12/906,001 filed Oct. 15, 2010, now U.S. Pat. No. 9,005,355, issued Apr.14, 2015, which application is herein incorporated by reference in itsentirety.

FIELD OF THE INVENTION

This invention relates to coating compositions having anticorrosionproperties and, more specifically, to coating compositions speciallyengineered to include an amorphous aluminum phosphate corrosioninhibiting pigment and methods for making the same.

BACKGROUND OF THE INVENTION

Coating compositions formulated to include one or more material toprovide anticorrosion properties, used for forming a film layer on thesurface of metallic substrates, are known in the art. Such coatingcompositions make use of materials known to provide some degree ofprotection against corrosion by one of three different mechanisms.

A first mechanism of corrosion control in coating compositions is oneprovided by a formulation where a binder composition, that imparts ahigh degree of moisture and water diffusion resistance to the resultingcured film, is combined with a pigment or solid component that enhancesthe barrier properties of the film composition, thereby providing aphysical barrier to any water passing into the cured coating film toprotect the underlying coated metal substrate surface from corrosion.Further, this coating film has a high degree of adhesion to the metallicsubstrate, primarily through the adhesion properties of the bindercomponent of the composition. Pigment materials or solid componentsuseful in facilitating the barrier properties of the compositioncomprising the film include aluminum, iron oxide, mica, talc, talc,calcium silicate, and barium sulfate in particle and/or flake form.

A second mechanism of corrosion control in coating compositions is oneprovided by the placement of a desired material adjacent the metallicsubstrate surface that is selected to sacrificially corrode upon contactwith any water and oxygen passing into the cured coating film, therebysacrificially corroding to cathodically protect and prevent theunderlying metallic substrate from corroding. Zinc metal is an examplematerial useful in this regard, and can be provided on the surface ofthe substrate as a constituent in a coating composition or can beprovided separately therefrom.

A third mechanism of corrosion control is one where the coatingcomposition makes use of a material that is corrosion inhibiting, e.g.,a corrosion inhibiting pigment, in that such material, upon beingcontacted with water, releases a material that diffuses to the substratesurface and either adsorbs on the substrate to form an impermeable layerwhich interferes with the corrosion reaction, or forms a reactionproduct with the surface of the metallic substrate or with the oxidelayer on the surface, thereby preventing the surface from reacting withwater, oxygen, and other corrosive materials. This operates to passivatethe substrate surface and thereby protect it from corrosion. Materialsknown to be useful in this regard include calcium zinc phosphomolybdate,aluminum triphosphate, zinc phosphate, zinc iron phosphate, strontiumzinc phosphosilicate, calcium phosphosilicate, zinc aluminum phosphate,lead-containing materials, and chromate-containing materials.

While anticorrosion coating compositions known in the art provide somedegree of protection against unwanted corrosion, such coatingcompositions may rely on the use of materials that present adanger/hazard to the environment and/or a health or safety hazard topeople and for these reasons the use of such coating compositions haveor are being restricted or prohibited altogether. Additionally, suchknown coating compositions, while providing some degree of corrosionprotection, are unable to provide a desired or needed level of corrosioncontrol that is sufficient to meet the demands of certain end-useapplications. The shortcomings of such known coating compositions can becaused by a failure of the particular corrosion control mechanism tooperate effectively under actual exposure conditions and/or afailure/breakdown in the film itself formed from the composition.

It is, therefore, desired that an anticorrosion coating composition beformulated in a manner that provides a desired degree of corrosioncontrol/resistance without the use of materials being regulated orotherwise known to present a hazard/danger to the environment and/orhealth or safety issues to people. It is desired that such anticorrosioncoating compositions be formulated in a manner that provides a desiredimproved degree of corrosion resistance and film performance propertieswhen compared to known coating compositions, thereby meeting the needsof certain end-use applications. It is further desired that suchanticorrosion coating composition be formulated from readily availablematerials, and/or be made according to a process, that facilitatesmanufacturing the coating composition in a manner that does not requirethe use of exotic equipment, that is not unduly labor intensive, andthat is economically feasible.

SUMMARY OF THE INVENTION

Anticorrosive coating compositions as disclosed herein comprise abinding polymer and aluminum phosphate dispersed within the bindingpolymer. The binding polymer can be selected from the group includingpolyurethanes, polyesters, solvent-based epoxies, solventless epoxies,water-borne epoxies, epoxy copolymers, acrylics, acrylic copolymers,silicones, silicone copolymers, polysiloxanes, polysiloxane copolymers,alkyds and combinations thereof. The aluminum phosphate comprisesamorphous aluminum phosphate. In a preferred embodiment, the aluminumphosphate is amorphous aluminum phosphate at the time that is itcombined with the binding polymer and at the time that the coatingcomposition is applied to a surface of a metallic substrate. The coatingcomposition comprises in the range of from about 1 to 25 percent byweight aluminum phosphate.

In an example embodiment, the coating composition provides a controlledphosphate delivery, e.g., of phosphate anions, in the range of fromabout 100 to 1,500 ppm. The phosphate delivery can come from thepresence of amorphous aluminum phosphate alone or as combined withammonium phosphate. In an example embodiment, the coating compositionhas total solubles content of less than about 1500 ppm, less than 800ppm, preferably less than about 400 ppm, and more preferably of fromabout 100 to 250 ppm. The amorphous aluminum phosphate is preferablysubstantially free of alkali metals and alkaline earth metals.Additionally, the aluminum phosphate has a water adsorption potential ofup to about 25 percent by weight water when present in a cured film.

The amorphous aluminum phosphate particles are aggregates of colloidalprimary particles, wherein the primary particles have an average size ofabout 1 to 100 nanometers. Both the colloidal and aggregate particlesare substantially spherical in shape, and have a substantially uniformsize distribution.

Amorphous aluminum phosphate useful for forming anticorrosion coatingcompositions is formed by sol gel process wherein an aluminum salt iscombined with phosphoric acid in an aqueous solution. A sufficientamount of base material is added to increase the pH of the solution toform a sol comprising a dispersion of colloidal amorphous aluminumphosphate particles in solution. A further amount of the base materialis added to cause the colloidal particles to aggregate and form a gelstructure, wherein the gel comprises a three-dimensional structure oflinked-together amorphous aluminum phosphate particles. In an exampleembodiment, the process of making the aluminum phosphate is specificallycontrolled to produce amorphous aluminum phosphate having the desiredengineered properties of controlled phosphate anion release with areduced/low solubles content.

The resulting amorphous aluminum phosphate is dried and/or thermallytreated, depending on the specific end-use applications. In oneembodiment, the amorphous aluminum phosphate is washed and dried attemperatures sufficient to only evaporate water, producing a resultingpowder that (when joined with a binding polymer) produces ananticorrosion coating composition having a relatively high phosphateanion controlled release of up to 1,500 ppm due in part to the presenceof ammonium phosphate. In another embodiment, the amorphous aluminumphosphate washed and thermally treated at temperatures between 200 and300° C., producing a resulting powder that (when joined with a bindingpolymer) produces an anticorrosion coating composition having a lowerphosphate anion controlled release due to the absence of ammoniumphosphate.

Such anticorrosion coating compositions can be used as a primer coat, amid-coat, and/or a top-coat coating depending on the particularformulation and/or end use application. The anticorrosion coatingcomposition can be applied to a metal substrate and allowed to dry toform fully-cured film. In the event that the binding polymer issolvent-borne, the amorphous aluminum phosphate in the cured filmcontrols corrosion of the underlying substrate by both adsorbing and/orabsorbing water entering the film and providing passivating phosphateanion.

Anticorrosion coating compositions as disclosed herein are formulated ina manner that provides a desired degree of corrosion control/resistancewithout the use of materials being regulated or otherwise known topresent a hazard/danger to the environment and/or health or safetyissues to people. Further, such anticorrosion coating compositions areformulated in a manner that provides a desired improved degree ofcorrosion resistance, when compared to known coating compositions,thereby meeting the needs of certain end-use applications. Suchanticorrosion coating compositions are formulated from readily availablematerials, and are made by processes, that facilitate manufacturing in amanner that does not require the use of exotic equipment, that is notunduly labor intensive, and that is economically feasible.

DETAILED DESCRIPTION

Anticorrosion coating compositions, and methods for making the same, aredisclosed herein. Such anticorrosion coating compositions are formulatedto include a desired amount of an amorphous aluminum phosphate corrosioninhibiting pigment that has been specially engineered to providecombined desired features of a controlled release/delivery of an optimumamount of passivating anion, e.g., phosphate anion, to inhibitcorrosion, and a controlled amount of total solubles. Further, thecorrosion control properties of said engineered aluminum phosphatecompositions are facilitated by the ability of the amorphous structureto increase the barrier properties of the composition by adsorbingdiffusing water in the film and/or by chemically bonding with functionalgroups of certain binders to increase the cross-link density, and hencebarrier properties, of the film. These features arise from the uniqueproperties of the particles formed as a result of the sol-gel synthesisprocess that is used to make the aluminum phosphate.

Together, such features permit anticorrosion coating compositions asdisclosed herein to provide an improved degree of corrosion resistanceto an underlying metallic substrate surface without compromising filmand composite integrity and stability, thereby offering such improvedcorrosion resistance for an extended service life when compared toconventional anticorrosion coating compositions. Conventionalanticorrosion coating compositions neither provide an adequatecontrolled release rate of passivating anion nor have a controlledamount of total solubles.

Amorphous aluminum phosphates used in these anticorrosion coatingcompositions are also specially designed to have a high level ofcompatibility with a variety of different binding polymers or bindingpolymer systems useful for forming such coating composition, therebyproviding a high degree of flexibility and choice in formulating theanticorrosion coating composition to meet the needs and conditions of avariety of end-use applications in a number of different end-useindustries. Current commercially available inhibitive pigments are veryoften either binder specific or substrate specific in their application,thereby limiting end-use applications.

Anticorrosion coating compositions comprise a desired binding polymerthat can be selected depending on the different end-use application aswell as other factors. Example binding polymers include those currentlyused for making known anticorrosion coating compositions, and can beselected from the general group including water-borne polymers,solvent-borne polymers, hybrids and combinations thereof. Examplewater-borne polymers useful for making anticorrosion coatingcompositions include acrylic and acrylic copolymers, alkyd, epoxy,polyurethane, and silicone, and polysiloxane polymers. Examplesolvent-borne and/or non-aqueous polymers useful for makinganticorrosion coating compositions include acrylic and acryliccopolymers, epoxy, polyurethane, silicone, polysiloxane, polyester, andalkyd. Preferred binding polymers include acrylic copolymer latex,alkyd, polyurethane and epoxy polymers.

In an example embodiment, anticorrosion coating compositions comprise inthe range of from about 15 to 75 weight percent, preferably in the rangeof from about 20 to 60 weight percent, and more preferably in the rangeof from about 20 to 35 weight percent of the binding polymer based onthe total weight of the coating composition. An anticorrosion coatingcomposition comprising less than about 15 percent by weight of thebinding polymer may include a greater amount of the corrosion inhibitingpigment than necessary to provide a desired degree of corrosionresistance. An anticorrosion coating composition comprising greater thatabout 75 percent by weight of the binding polymer may include an amountof the corrosion inhibiting pigment that is insufficient to provide adesired degree of corrosion resistance. While certain amounts of thebinding polymer have been provided, it is to be understood that theexact amount of the binding polymer that is used to formulateanticorrosion coating compositions will vary depending on such factorsas the type of binding polymer used, the type and/or quantity ofinhibiting pigment that is used, and/or the particular end-useapplication, e.g., the substrate to be coated and the corrosiveenvironment intended for the substrate.

Corrosion inhibiting pigments useful for making anticorrosion coatingcompositions comprises phosphate-containing compounds. Preferredphosphate-containing compounds are aluminum phosphates. Aluminumphosphates useful in this regard include amorphous aluminum phosphates,crystalline aluminum phosphate, and combinations thereof. Preferredaluminum phosphates are amorphous aluminum phosphates, and mostpreferred aluminum phosphates are amorphous aluminum orthophosphates.The use of amorphous aluminum phosphates is preferred because amorphousaluminum phosphates, as specially engineered herein, provide acontrolled release rate of phosphate anion, when diffusing watercontacts the pigment in the coating, sufficient to provide passivationto the metal substrate.

Further, it has been found that amorphous aluminum phosphatecompositions can be engineered having a soluble material content that issufficiently low such that total solubles do not cause osmoticblistering of a cured film when such film is contacted with water.Accordingly, amorphous aluminum phosphates as used in anticorrosioncoating compositions as disclosed herein are specially engineered toprovide both a controlled release or delivery of passivating anion,e.g., phosphate anions, to inhibit corrosion, and to have a low totalsolubles content to avoid osmotic blistering to ensure extended filmintegrity.

In an example embodiment, the amorphous aluminum orthophosphates areamorphous aluminum hydroxy phosphates. Amorphous aluminum hydroxyphosphates are preferred because they provide uniform dispersionproperties within the composition and the dispersion remains stablethroughout the shelf-life of the formulation. The hydroxyl content ofthe amorphous aluminum hydroxy phosphate is the unique functional groupthat provides matrix stability by providing hydrogen bonds with suitablegroups of the binding polymer of the formulation, e.g., such as carboxylgroups, amino groups, hydroxyl groups, acid groups and the like. Thisfeature is unique to the amorphous aluminum hydroxy phosphate and is notpresent in crystalline aluminum phosphates.

Anticorrosion coating compositions are formulated to contain a specificamount of the inhibiting pigment calculated to provide a sufficientamount of the passivating anion when placed into end use to inhibitcorrosion. In an example embodiment, the anticorrosion coatingcomposition comprises in the range of from about 3 to 25 weight percent,preferably in the range of from about 5 to 15 weight percent, and morepreferably in the range of from about 8 to 12 weight percent of theamorphous aluminum phosphate based on the total weight of the coatingcomposition dry film. An anticorrosion coating composition comprisingless than about 3 percent by weight of the amorphous aluminum phosphatemay contain an amount that is insufficient to provide a desired degreeof corrosion resistance. An anticorrosion coating composition comprisinggreater that about 25 percent by weight of the amorphous aluminumphosphate may include an amount more than necessary to provide a desireddegree of corrosion resistance, and such additional amount can operateto impair long-term stability and/or integrity of the cured coatingfilm. While certain amounts of the amorphous aluminum phosphate havebeen provided, it is to be understood that the exact amount of theamorphous aluminum phosphate that is used to formulate anticorrosioncoating compositions will vary depending on such factors as the typeand/or quantity of binding polymer used, and/or the particular end-useapplication, e.g., the substrate to be coated and the corrosiveenvironment intended for the substrate

As briefly noted above, the amorphous aluminum phosphate is speciallyengineered to provide a controlled release or delivery of one or morepassivating anions upon being contacted with water and oxygen, when thecoating composition is applied to the surface of a metallic substrate,formed into a cured film, and placed into a corrosive environment. Overtime, water/moisture and certain corrosive salts migrate or diffuse intothe applied coating film, which water comes into contact with thephosphate component that is available in the film. Such contact withwater promotes release/delivery of phosphate anion from the amorphousaluminum phosphate in a controlled manner. These phosphate anions reactwith iron species of the surface of the underlying metallic substrate toform a passivating film thereon that operates to form a barrierprotecting the underlying metallic surface from corrosion. A feature ofthe amorphous aluminum phosphates used to make anticorrosion coatingcompositions disclosed herein is that they are engineered torelease/deliver a controlled amount of the phosphate anions.Specifically, to release/deliver an amount of the phosphate anionscalculated to provide an optimum level of corrosion protection withoutsacrificing other coating cured-film performance properties that mayotherwise compromise the effective film service life.

Currently phosphate-based inhibitive pigments are derived in somefashion from zinc phosphate. The latter material has the disadvantage ofa low release rate, and the release rate is dependent on conditionsexisting in the service environment. To accommodate this deficiency,zinc phosphate has been modified with other components such as aluminum,strontium, calcium to facilitate phosphate release properties and toprovide secondary or companion passivation mechanisms, typicallyproviding a component that precipitates onto the substrate to providecathodic passivation. These approaches provide some benefit by improvingperformance compared to zinc phosphate, but they do not reach thedesired level of improvement described above. The amorphous aluminumphosphate compounds described herein optimize the anodic passivationmechanism in a manner not achieved by any other phosphate-based pigment.

In an example embodiment, anticorrosion coating compositions asdisclosed herein comprising amorphous aluminum phosphate are engineeredto release a controlled amount of passivating phosphate anion whenpresent in a cured film placed into an end-use application that isexposed to moisture. The controlled amount can vary depending on suchfactors as the method that is used to make the aluminum phosphate, thebinding polymer system, and the particular end-use application. In anexample embodiment, coating compositions can be engineered to provide arelatively high controlled phosphate anion release of 1,500 ppm or less,preferably between about 600 to 1,200 ppm, and more preferably betweenabout 800 to 1,000 ppm. Such high level of controlled phosphate anionrelease can be useful in coating systems comprising a solvent-bornebinding polymer such as epoxy and the like with low moisture vaportransmission rates (MVT), that are not as susceptible to suffering filmbreakdown due to relatively high solubles levels. The ability to providea coating composition having such a high level of controlled phosphateanion release is desirable for end-use applications placed intoaggressive corrosion environments where high levels of passivating anionmay be required to protect against corrosion where physical breaks orvoids occur in the coating film.

In another example embodiment, coating compositions can be engineered toprovide a controlled phosphate anion release of 500 ppm or less,preferably between about 50 to 500 ppm, more preferably between about100 to 200 ppm. Such level of controlled phosphate anion release can beuseful in coating systems comprising a water-borne binding polymer suchas latex and the like with higher MVT, that can be more susceptible tosuffering film breakdown due to relatively high total solubles levels.The ability to provide a coating composition having such level ofcontrolled phosphate anion release is desirable for end-use applicationsplaced into less aggressive corrosion environments.

The amount of passivating anion to be delivered depends on a number ofdifferent factors such as the loading or amount of the amorphousaluminum phosphate used to make the anticorrosion composition, the typeof binding polymer that is used, the type of metallic substrate beingprotected, and the type of corrosion environment present in the end-useapplication. In one example embodiment, where the metallic substratebeing protected comprises iron and the corrosion environment compriseswater, oxygen, and other corrosive salts, the amorphous aluminumphosphate is engineered to release approximately 160 ppm of thepassivating phosphate anion.

An amorphous aluminum phosphate having a controlled release less thanabout 50 ppm of the passivating anion may not provide a sufficientamount of the passivating anion to inhibit corrosion for the desiredservice life. An amorphous aluminum phosphate having a controlledrelease greater than about 1,500 ppm of the passivating anion, whileproviding a level sufficient to inhibit corrosion, may provide too higha level of total solubles that can cause blistering or other unwantedeffects in the cured film that can impair its long term integrity andstability, thereby possibly reducing effective service life.

Anticorrosion coating compositions are engineered having a controlled orminimized level of solubles. As used herein, the term “solubles” and“nonpassivating solubles” are used interchangeably to refer to materialsusually produced as a byproduct of making the amorphous aluminumphosphate and can include alkali metals such as sodium, potassium, andlithium, and such anions as sulfates, chlorides and nitrates, and isunderstood to not include the passivating anions, present in theamorphous aluminum phosphate. In a preferred embodiment, the amount ofnonpassivating solubles is zero. A maximum amount of nonpassivatingsolubles is 250 ppm.

It has been discovered that the presence of such solubles, if leftunchecked, can operate to impair the stability and/or integrity of theanticorrosion coating composition and/or the cured film formedtherefrom, thereby adversely affecting its intended service life. Forexample, the presence of such solubles has been found to result inunwanted blistering, delamination from the substrate, under-filmcorrosion and other types of unwanted film failures when exposed tocertain corrosive environments, which film failures operate to exposethe underlying metallic substrate surface leaving it unprotected.

In an example embodiment, it is desired that the anticorrosion coatingcomposition comprise less than about one percent (or less than 10,000ppm) of total solubles, i.e., solubles including phosphate passivatinganion, preferably less than about 1,500 ppm total solubles, and morepreferably less than about 400 ppm total solubles. In an exampleembodiment, the anticorrosion coating composition comprises in the rangeof from about 50 to 800 ppm total solubles, and preferably in the rangeof from about 100 to 250 ppm total solubles. Anticorrosion coatingcompositions comprising less than about 400 ppm total solubles producecured films that, when subjected to end use corrosive environments, donot demonstrate blistering or other unwanted film events, therebyoperating to enhance effective service life. Accordingly, a feature ofanticorrosion coating compositions is that, in addition to providing acontrolled release of passivating anion, they are specially engineeredto have a reduced amount of total solubles to ensure an intended servicelife.

A feature of this invention derived from the ability to provide aluminumphosphate inhibitive pigments with controlled release and suitablesoluble levels, is the ability to formulate coating compositions withphosphate release rates tailored for specific applications. For example,it has been found that epoxy-polyamide based coating compositions canaccommodate higher levels of total solubles than an acrylic latexcomposition. This has been found to be especially beneficial inproviding improved protection against corrosion at edges, defects, andphysical breaks in the coating film. Having higher levels of phosphateavailable in these circumstances facilitates anodic passivation andprotects wet adhesion.

Aluminum phosphates useful in anticorrosion coating compositions asdisclosed herein are specifically engineered to have uniformly sphericalshapes, to have nanosized (10⁻³μ or 100 nanometers) primary particleswith high surface area and micro-porosity, and to have anarrow/substantially uniform particle distribution when aggregated. Theuniformity in shape and size is desired for the purpose of facilitatingmixing and uniform dispersion of the aluminum phosphate particles in thebinding polymer, thereby promoting uniform corrosion resistanceperformance of the coating composition and cured film formed therefrom.In an example embodiment, the spherical shape of the aggregate particlesis obtained by using a sol-gel synthesis method as disclosed herein, andby controlling certain processing steps in the method of making thealuminum phosphate, e.g., by specifically avoiding shear agitation whichcan produce undesired aluminum phosphate plate or sheet-shapedparticles.

The dried aluminum phosphate particles have a substantially uniformprimary particle size distribution of between about 10 to 100nanometers, wherein D99 is approximately 100 nanometers, and D50 isapproximately 50 nanometers. The particle size distribution ofaggregated primary particles after milling ranges from about D99 of 6μto D50 of 2μ. Producing aluminum phosphate particles having asubstantially uniform particle size distribution is desired to promoteuniform particle dispersion in the binding polymer to produce uniformcorrosion performance within the coating composition.

Aluminum phosphate useful in anticorrosion coating compositions asdisclosed herein are specifically engineered to having relatively highsurface areas that can be characterized by a variety of methodsincluding BET measurement (m²/gram) and mercury porosimetry. In anexample embodiment, the aluminum phosphate has a surface area of greaterthan about 100 m²/g, preferably between about 125 m²/g to 150 m²/g, andmore preferably between about 125 m²/g to 135 m²/g. The surface area ofthe aluminum phosphate is controlled by the sol-gel synthesis reactionand by the particular process that is used to treat the aluminumphosphate solid after formation by the sol gel process, which processand treatment is better described below.

Sol Gel Method of Making

Generally, the amorphous aluminum phosphate is a phosphate complex inwhich the nucleating cation is aluminum alone, or aluminum incombination with other multi-valent cations such as calcium, magnesium,barium and the like. It is desired that a method of making the amorphousaluminum phosphate be one that produces amorphous aluminum phosphatefree of all other metal cations, e.g., especially free of alkali metalcations, for the purpose of reducing/eliminating the existence ofunwanted solubles in the resulting anticorrosive coating composition.

In an example embodiment, the amorphous aluminum phosphate is preparedby a sol-gel process that involves the creation of inorganic molecularnetworks from molecular or ionic precursors through the formation of acolloidal suspension (sol) and the gelation of such sol to form a solidnetwork in a continuous liquid phase (gel). The precursors forsynthesizing these colloids typically comprise a metal or metalloidelement surrounded by various reactive groups. Stated another way, inthe sol gel process, simple molecular or ionic precursors are convertedinto nano-sized particles to form a colloidal suspension (sol). Thecolloidal nano-particles are then linked with one another in athree-dimensional liquid filled solid network (gel). This transformationto a gel can be initiated in a number of ways, but the most convenientapproach is to change the pH of the reaction solution.

The method used to remove the liquid from the solid will affect the solgel's properties. For example, supercritical drying will maintain thethree-dimensional structure in the dried solid, whereas slow drying in afluid evaporation process collapses the network structure creating ahigh density material.

Advantages to preparing the amorphous aluminum phosphate via a sol gelsynthesis process, as opposed to, for example, a precipitation process,include process versatility and simplicity resulting in the possibilityto obtain highly pure and/or tailored materials, uniform particle sizedistribution, substantially spherical-shaped aggregate particles,nano-sized particles, and custom engineered compositions. Whileamorphous aluminum phosphate as disclosed herein comprises substantiallyspherical aggregate particles, it is understood that some small amountof nonspherical particles may unintentionally be produced and may bepresent in the resulting anticorrosion coating compositions. Forexample, the sol gel process provides alkali-metal free amorphousaluminum phosphate of high surface area which provides an optimum amountof phosphate anion when the material is contacted with water to providepassivation to steel thereby preventing corrosion.

As used herein, the term “gel” is understood to be a three-dimensionalcage structure formed of linked large molecular mass polymers oraggregates in which liquid is trapped. The network of the structuretypically consists of weak and/or reversible bonds between the coreparticles. The term “sol” as used herein is understood to be a colloidaldispersion of solids in a liquid. The solids comprise aluminum phosphatehaving nanometer scale average particle sizes. The gel comprises analuminum phosphate sol as a dispersed phase in a semi-rigid massenclosing all of the liquid. Post treatment of product produced by thesol gel process by filtration, washing, drying, and combinations thereofleads to aggregation of the colloidal solids in a controlled fashion toform a larger solid complex.

Generally, the sol gel process includes the following process steps: (1)nucleation or polymerization or condensation of the molecular precursorsto form primary particles, e.g., nanometer in scale, to form the sol(colloidal dispersion or suspension); (2) growth of the particles orgelation; (3) linkage of the particles to form chains and the extensionof such chains throughout the liquid medium to form a thickened gel; and(4) treating the sol gel material to remove the liquid to give a desiredsolid end-product.

In an example embodiment, the precursor solution is prepared bycombining a suitable aluminum source, with a phosphorous source.Suitable aluminum sources can be selected from the group of aluminumsalts such as aluminum chloride, aluminum nitrate, aluminum sulfate andthe like. A preferred aluminum source is aluminum nitrate. Phosphoroussources useful for forming amorphous aluminum phosphate by sol gelprocess include phosphoric acid, and salts of phosphorus asorthophosphates or as polyphosphates. A source of phosphorus isfertilizer grade phosphoric acid, from any origin, that has beenclarified and discolored.

The primary ingredients of the precursor solution are combined togetherin an aqueous environment with a gelling agent to produce a colloidaldispersion of solid aluminum phosphate particles in solution. In anexample embodiment, the precursor solution is formed by combiningaluminum nitrate with phosphoric acid (85% by weight) in the presence ofwater. Water can be present in one or more of the aluminum nitrate, thephosphoric acid, or as added water independent of either ingredient.

After the precursor ingredients are combined, the resulting system isstirred and a suitable alkaline ingredient is added to the stirredsolution. Alkaline ingredients useful for this purpose include thoseconventionally used to change the pH of the system, e.g., increase thepH of the acidic system, and in an example embodiment is ammoniumhydroxide. In a preferred embodiment, it is desired that the alkalinesolution be alkali metal fee. The presence of the ammonium hydroxideincreases the pH and drives the process of nucleation and condensationforming a colloidal dispersion or sol. Depending on the concentration ofnucleating agent, this step can be intermediate or final. Furtheraddition of nucleating agent causes the primary aluminum phosphateparticles to link together forming a gel, e.g., results in gelation, andfurther results in the colloidal particles being linked into the gelstructure to form a sol gel.

In an example embodiment, it may be desired to control the sol gelprocess to isolate the colloidal dispersion before gelation. This can bedone by controlling the reaction conditions so that only colloidaldispersion occurs (i.e., formation of a sol) and not full gelation.Controlling the process in this manner may provide certain manufacturingadvantages and/or provide certain advantages relating to handling of theend-product. The colloidal dispersion from this process can be filteredto recover the solids, and then thermally treated and/or washed asdescribed below.

In an example embodiment, the phosphoric acid, aluminum nitrate, and/orammonium hydroxide can be heated prior to being combined with oneanother, or can be heated after combination, e.g., during stirring.Additionally, the amount of water present and/or the rate of addition ofthe ammonium hydroxide, can be adjusted to produce a desired reactionproduct having a desired yield of amorphous aluminum phosphate.

In an example embodiment that amount of ammonium hydroxide, NH₄OH, thatis added to the acid solution is sufficient to neutralize the acidsystem to initiate formation of colloidal aluminum phosphate particles,and for gelation exceeds the stoichiometric amount to form ammoniumnitrate, NH₄NO₃. The range can be from the stoichiometric amount ofNH₄OH needed to form the NH₄NO₃ (1.0 stoichiometry) to about 3.0stoichiometry, preferably between about 1.1 and 2.0, and more preferablybetween about 1.2 and 1.5.

The order of addition (i.e., base solution to acid precursor solution orvice versa) has been found to control the rate and extent of gelation.When base is added to stirred precursor solution in stoichiometricconcentration ranges stated above (1.0 to 3.0) virtually instantaneousgelation occurs. It has been discovered that reversing the order ofaddition, i.e., adding the precursor solution to the base solution,provides control over the extent of growth from colloidal dispersion tofull gelation. As discussed below, it has also been discovered thatparticle morphology can be controlled by the method of addition.

It has been found that concentrations of ammonia in excess of the 1.1stoichiometric ratio are useful to minimize unreacted aluminum in theresulting complex. For the end-use application as an inhibitive pigment,it is desirable that the phosphate release rate from the complex whencontacted with water be in the 200 to 400 ppm range. Testing hasdetermined that phosphate anion elution is in the target range when theammonia level in the reaction is around 1.2 to 3.0 stoichiometric ratioand after the solid has been thoroughly washed and/or thermally treatedto remove the soluble by-products as described below.

In an example process, the sol gel is next subjected to post gelationtreatment which may comprise heating, washing, and/or sizing. In anexample embodiment, the sol gel powder formed is isolated by collapsingthe dispersion or gel by driving off the liquid constituent. Varioustypes of gels can be formed from the sol gel such as; xerogels that aresolids formed by unhindered drying of the sol gel so as to yield highporosity and surface area (150-1,000 m²/g) in solid form, aerogels thatare solids formed by supercritical drying (e.g., freeze drying),hydrogels that are water insoluble colloidal polymer particles dispersedin water, and organogels that are amorphous, non-glassy solidscomprising a liquid organic phase trapped in the solid matrix.

The sol gel consists of solid AlPO₄ connected through various pHdependent (amino, water, phosphate) linkages to form a solid dispersedphase as a mass enveloping all the liquid, the latter consisting ofwater and dissolved salts. Heating the gel, to a temperature above about100° C., evaporates the water and any ammonia and collapses the mass toa solid consisting of aluminum phosphate, AlPO₄, and ammonium nitrate,NH₄NO₃. Heating the gel or the collapsed gel solid, to a temperatureabove about 215° C., thermally decomposes the ammonium nitrate, NH₄NO₃,thereby eliminating it from the powder product. Heating to temperaturesabove about 215° C. leads to a decrease in pH, indicating that residualamino groups remaining after thermal decomposition of the ammoniumnitrate, NH₄NO₃, most likely as substituents on the PO group, are alsothermally decomposed and replaced by hydrogen atoms thereby making thecomplex acidic. The solid product resulting from this treatment has beenshown by analysis to be pure amorphous aluminum phosphate having aphosphate release rate of around 240 ppm and surface area greater than125 m²/gram.

Accordingly, the post gelation heat treatment can comprise a single stepof heating the sol gel to a relatively high temperature above about 250°C. for a period of time sufficient to achieve water evaporation,collapsing of the mass, and thermally decomposing the ammonium nitrate,NH₄NO₃. In an example embodiment, this can be done at about 250° C. forapproximately 12 to 72 hours. The resulting product from this heattreatment is substantially aluminum phosphate, i.e., there is verylittle if any ammonium phosphate or ammonium nitrate. Accordingly, thecontrolled phosphate anion release for aluminum phosphate treated inthis manner is 250 ppm or less as noted above.

Alternatively, the post gelation heat treatment can comprise a singlestep of heating the sol gel at a lower temperature of about above about100 to 150° C. for a period of time sufficient to achieve waterevaporation. In an example embodiment, this can be done at about 110° C.for approximately 1 to 24 hours. The resulting product from this heatingor drying treatment is aluminum phosphate and ammonium phosphate andammonium nitrate. The amount of ammonium phosphate present in theresulting product is up to about 1,000 ppm.

This drying step can be followed by a heat treatment step at atemperature of between about 215 to 300° C. In a preferred embodiment,the drying step is at about 110° C. for about 24 hours, and the heattreatment is about 250° C. for up to 1 to 3 days (16 to 72 hours). Theresulting solid has a moisture content of from about 5 to 20 percent byweight. The pH of the heat treated material can be adjusted byre-dispersing the complex and adjusting the pH with ammonium hydroxidesolution. The resulting complex is then dried at 100 to 110° C. toremove water and ammonia.

If desired, before drying or heat treatment, the sol gel material can befiltered to separate the solid particles from solution, and theseparated solid, e.g., in the form of a cake, can be subjected to one ormore wash cycles. The wash cycles use water and operate to rid the solidaluminum phosphate particles of any unwanted solubles, e.g., ammoniumcompounds such as ammonium nitrate, and ammonium phosphate that havebeen formed as a reaction by-product. The washing step removes freeammonium salts, however, ammonium phosphate bonded to the aluminumphosphate survives. The washed sample can then be dried and/or heattreated in the manner disclosed above to further evaporate water and/orthermally decompose any residual ammonium nitrate and ammonium phosphatein the washed aluminum phosphate, and densify the aluminum phosphateparticles.

If desired, the sol material can be dried at about 100° C. to evaporatewater and collapse the mass, and the collapsed powder can be washed withwater to remove ammonium nitrate, NH₄NO₃, to thereby recover instead ofthermally decompose the by-product. The washed and dried mass can beheat treated above about 215° C. to thermally decompose any residualammonium nitrate, NH₄NO₃, thereby providing substantially pure amorphousaluminum phosphate, free of residual soluble salts.

The basic chemistry of the sol gel process is presented below asfollows:

1. Precursor solution—Combination of all ingredients

Al(NO₃)₃.9H₂O+H₃PO₄+H₂O

2. Gelling Agent

3NH₄OH+H₂O

3. Sol-gel reaction

Reaction to form amorphous aluminum phosphate sol gel: as NH₄OH (28% NH₃in water) is added, it neutralizes the acid system and drives formationof insoluble ALPO₄ 4, that takes Al⁺³ out of the reaction and allowsmore NH₄ ⁺¹ to combine with NO₃ ⁻¹ to form soluble NH₄NO₃. Depending onthe concentration and rate of addition of the NH₄ 4 OH colloidalparticles of AlPO₄ will form. Adding more NH₃ to the reaction allows theAlPO₄ colloidal particles to aggregate and to eventually form bondsbetween the particles to form the gel structure. The amount of NH₃ addedmust exceed the stoichiometric amount required to form NH₄NO₃ in orderto have sufficient NH₃ to control pH and facilitate gel bridging.Depending on the amount of NH₃ added, the rate of addition, and theconcentration, the gel will consist of a mass of AlPO₄ solid particleslinked forming a cage, three-dimensional structure encapsulatingammonium nitrate, NH₄NO₃, dissolved in water. Ammonium phosphate mayalso be present as an intermediate, and extending reaction conditions(i.e., by further heating) will lead to full reaction with the aluminumin the system to condense to aluminum phosphate.

AlPO₄+(NH₄)₃PO₄+H₂O→AlPO₄+NH₄OH

4. Filtration and washing—Optional to supplement or replace thermalpurification to remove soluble ammonium salts.

5. Dehydration and drying—Drying at above at least 100° C. to evaporatewater and collapse the sol gel structure to form a densified solid.

AlPO₄+NH₄NO₃

6. Thermal purification—Thermal treatment at 215 to 250° C. to thermallydecompose ammonium nitrate.

AlPO₄ (amorphous aluminum phosphate)

If desired, the order of ingredient addition can be changed from thatdisclosed above. For example, the acid solution may be added to asolution of the ammonium hydroxide in order to control the viscosity ofthe reaction system and/or impact the surface area of the colloidalsolids. Such flexibility in the order of ingredient addition may beadvantageous, e.g., for the scale-up of manufacturing where it may bedesirable to avoid gelation in favor of the formation of a suspension ofcolloidal primary particles. The resulting composition after washing,drying and/or thermal treatment is essentially chemically the sameregardless of the order of addition. However product morphology isaffected by these processing parameters. Adding acid to base results inhigher surface area and greater porosity. The sol gel process disclosedherein produces an aluminum phosphate composition consisting essentiallyof amorphous aluminum phosphate.

Base-to-acid sequencing causes rapid pH change and the rapid formationof sol particles followed by rapid gelation to form interlinkedparticles in the gel matrix. This reduces molecular mobility andprevents any further particle growth or morphological change. When acidis added to base, the pH change is slower and localized colloidalaluminum phosphate particles form. No gelation occurs so the systemmobility allows for continued competing side reactions (increasedsolublization of ammonium nitrate and ammonium phosphate) allowingintermediate species to survive. When dehydration and thermaldecomposition occur, small particles of aluminum phosphate exist in thepresence of departing water and decomposition products (of ammoniumnitrate), leading to more porosity in small aggregated aluminumphosphate particles.

As noted above, amorphous aluminum phosphate prepared by such sol gelprocess is substantially free of alkali metals and other unwantedsolubles, and provides a desired controlled release of passivatingphosphate anion, thereby greatly minimizing or eliminating the unwantedformation of film blistering and providing enhanced corrosion controlboth underfilm and at scribes in the film when compared to precipitatedaluminum phosphates.

The sol gel process disclosed above is provided as an exampleembodiment, and it is to be understood variations of preparation otherthan those specifically disclosed may be used. The following sol gelpreparation example is provided as reference.

The sol-gel process described herein produces amorphous aluminumphosphate pigments having surface areas (between about 100 and 150 m²/gBET) and very narrow particle size distributions compared to pigmentsproduced by other synthesis routes such as precipitation, which givessurface areas as low as 3 up to, typically, 30 m²/g BET. This feature ishighly desirable for an inhibitive pigment because the phosphate releasereaction is surface area dependent and the smaller, narrow particlesizes distribution ensure uniform dispersion throughout the film formedfrom the composition.

Example No. 1

In an example embodiment, amorphous aluminum phosphate having theabove-noted engineered properties is prepared by sol gel process basedon using approximately 100 grams of process material. Approximately567.5 grams of aluminum nitrate and approximately 174.4 grams phosphoricacid (85 weight percent) were dissolved in amounts of water noted belowwith mechanical stirring that does not introduce high shear. 1000milliliters of ammonium hydroxide (28 to 30 percent by weight NH₃) wasadded into the stirred solution. The solution was stirred for 1 hour atroom temperature before being processed for post heat treatment. TheP:Al ratio was fixed at 1.0. Different samples were made using the sameparameters but with different amounts of solvent water (250 grams, 500grams, and 2,000 grams). Additionally, different samples were made usingthe same parameters but with different rates of ammonium hydroxideaddition (10 mL/min. 100 mL/min, and 1,000 mL/min).

The following samples produced an amorphous aluminum phosphate sol gel;250 grams solvent water at 100 and 1,000 mL/min ammonium hydroxide; and500 grams solvent water at 1,000 mL/min ammonium hydroxide, and 2,000grams solvent water at 100 and 1,000 mL/min ammonium hydroxide. Some ofthe so-formed sol gel samples were thermally treated at 100° C. for 24hours before being heated to 250° C. for up to 2 to 3 days. Some of theso-formed samples were filtered, and the filter cake was washed withwater. The washed sample was thermally treated at 100° C. for 24 hours.The amorphous aluminum phosphate prepared according to this example wasalkali-metal free, was substantially free of solubles (having a solublecontent as disclosed above), and displaced the desired controlledrelease rate of phosphate anion (as disclosed above).

It was discovered that post-treatment (washing versus heating only to250° C.) has a controlling effect on the composition and structure ofthe amorphous aluminum phosphate formed. Heated samples (heated to 250°C.) give eluent having P:Al molar ratios close to 1.0 when they areeluted with water and are moderately acidic (around pH 3) indicatingthat the bulk material is essentially pure aluminum phosphate.Washed-only samples release more phosphate and less aluminum than theheated samples and are moderately basic in water (pH around 8). Thisindicates that the washed only samples have ammonium phosphate remainingin the bulk as either free or complexed with the aluminum phosphate.

Surface area of the solid is dependent on post-treatment, i.e., washingversus heating. The BET surface area of the heated (heated to 250° C.)solid is typically around 120 to 140 m²/g, whereas the samplecomposition washed-only as described above will have a surface area of80 to 90 m²/g. It was discovered that washing changes the stability ofthe particles in the colloidal dispersion. Typically, ionic chargesstabilize in the sol-gel structure to prevent agglomeration (whichmaintains small particle size and therefore high surface area). However,washing removes the ions thereby allowing agglomeration.

It was also discovered that the pH during the sol-gel reaction (i.e.,amount of ammonia present) will affect the nature of the particlesformed. Reaction and gel formation proceed at roughly the same rate.However, particles formed using low ammonium hydroxide ratios aresmaller and more easily dispersed in water after each wash. This resultsin a lower aluminum phosphate yield. The reaction changes from basecatalyzed to acid catalyzed when the ammonium hydroxide ratio is below1.5×. This leads to an “open” network structure which further hydrolyzesand condenses. The acid catalyzed reaction produces “finer” particlesthat are less linked.

A base catalyzed reaction creates a stable transition state that fullyhydrolyzes before condensation, leading to highly cross-linked particlesthat link to form gels with large pores between interconnectedparticles. During the synthesis process, it was found that a solid withthe lowest phosphate release is formed when the maximum amount of wateris used in the reaction system and the acid addition time to the base isthe shortest.

A feature of amorphous aluminum phosphate prepared by sol gel process asdescribed herein is that it produces nano-sized colloidal particles thatare spherical when aggregated and having a uniform particledistribution. Specifically, amorphous aluminum phosphate formed in thismanner has an average primary particle size in the range of from about 5to 100 nanometers, preferably in the range of from about 25 to 75nanometers, and more preferably in the range of from about 40 to 50nanometers. Amorphous aluminum phosphate particles sized less than about5 nanometers may interfere with the processing of coating formulationsand adversely affect film properties by increasing binder resinabsorption.

Enhanced control over the essential characteristics of amorphousaluminum phosphate is achieved by manipulating the amount,concentration, rate of addition, and/or order of addition of the pHcontrolling agent, e.g., the ammonium hydroxide, which operates toadjust and fine tune sol formation and gelation, thereby promoting theformation of an amorphous aluminum phosphate capable of providing adesired controlled delivery of passivating anion. Additionally, themethod of making as noted above provides an inherent process ofcontrolling unwanted solubles content, as there are no alkali metalsproduced and the presence of other solubles can be removed duringwashing and/or thermal treatment, thereby promoting formation of acoating composition having a desired film stability and integrity.

Amorphous aluminum phosphates prepared as noted above are preferably notsubjected to high-temperature treatment (above about 300° C.) for thepurpose of retaining the amorphous structure and avoiding conversion toa crystalline structure. It has been discovered that amorphous aluminumphosphates formed in this manner retain the desired amorphous structure,even after the above-disclosed drying and thermal treatment, and thisstructure provides a distinct benefit/feature for use as a corrosioninhibiting pigment.

Such amorphous aluminum phosphates display a markedly increased wateradsorption potential or degree of rehydration when compared tocrystalline aluminum phosphates, that permit such amorphous aluminumphosphates, once dehydrated by drying, to be rehydrated to contain up toabout 25 percent by weight water. This feature is especially useful whenthe amorphous aluminum phosphate is used with anticorrosion coatingcompositions, especially those comprising a non-aqueous composition. Insuch coating compositions the amorphous aluminum phosphate acts, inaddition to being a corrosion inhibiting pigment, as a moisturescavenger to both slow water intrusion into the cured film and restrictwater diffusion through the cured film. Thus, this water adsorptionfeature operates to provide another moisture barrier mechanism ofcorrosion control. The benefit of this effect has been demonstrated bythe use of electroimpedence spectroscopy (EIS).

Anticorrosion coating compositions are prepared by combining a selectedbinding polymer with the amorphous aluminum phosphate in the amountsdescribed above. The amorphous aluminum phosphate can be provided forcomposition formulation in the form of a dried powder or can be providedin the form of a slurry or liquid suspension depending on theformulation conditions or preferences.

Table 1 presents an example anticorrosion coating compositionformulation in the form of an epoxy-polyamide primer compositionprepared in the manner disclosed herein for purposes of reference.

TABLE 1 Example Epoxy-Based Anticorrosion Coating Composition SolventBased two parts Epoxy Primer Formula Part 1 Epoxy resin 238 lbs Additive3 lbs Pigment dispersant 5 lbs Solvent 1 75 lbs Solvent 2 20.4 lbsAnti-settling additive 10.2 lbs Red iron oxide pigment 120.4 lbsAnticorrosive pigment 150 lbs Extender pigment 1 341.3 lbs Extenderpigment 2 120.3 lbs Extender pigment 3 78.5 lbs Disperse high speed toHegman 5-6 Epoxy resin 24.8 lbs Solvent 96.3 lbs Part 2 Curing agent142.2 lbs

In this example, the first epoxy resin is a liquid epoxy resin based onthe di-glycidyl ether or bis-phenol A such as EPON 828 (HexionChemical), the additive is an polymer that facilitates flow-out in filmformation (Cytec), the pigment dispersant is an additive such asAnti-terra U (BykChemie), solvent 1 is an aromatic solvent such astoluene or xylene, solvent 2 is glycol ether, the anti-settling additiveis a thixatrope such as Bentone SD, the prime color pigment is red ironoxide, the anticorrosive pigment is the amorphous aluminum phosphateprepared by the method of making disclosed above and is provided in theform of a dried powder, extender pigment 1 is barium sulphate, extenderpigment 2 is magnesium silicate, extender pigment 3 is mica, the secondepoxy resin is the same as the first addition, the third solvent isxylene, and the curing agent is polyamide resin such as EPIKURE 3175(Hexion). The loading of the amorphous aluminum phosphate wasapproximately 10 percent by weight based on the total weight of thecomposition. Additionally, variations of this example formulation areprepared at amorphous aluminum phosphate loading levels of 5 and 15weight percent.

The epoxy-based example samples were studied using electro-impedancespectroscopy (EIS). An unexpected result from the EIS testing was theobservation that the incorporation of up to 15% by weight amorphousaluminum phosphate in epoxy-based samples demonstrated increasedimpedance in the epoxy film by up to an order of magnitude compared tocontrol. This result indicates that the amorphous aluminum phosphate inthese samples is enhancing the barrier properties of the epoxy by actingas a water scavenger, removing diffusing water from the matrix.

As water penetrates into the film, it is attracted to and accumulated atthe amorphous aluminum phosphate particles present in the film. Thewater is preferentially adsorbed by the amorphous aluminum phosphate andonly after local particle saturation has occurred will any water proceedbeyond that location in the film. When this occurs, the next layer ofamorphous aluminum phosphate will adsorb the water. This significantlyslows the diffusion of water through the film and thereby increases theservice life of the film. Further, the presence of water around there-hydrated, saturated amorphous aluminum phosphate particles results inthe release of phosphate anion into the migrating water. Hence, even ifthe service life is sufficiently long to allow diffusion of waterthrough the film to the substrate, the aqueous solution reaching thesubstrate will contain passivating phosphate anion thereby preventingcorrosion of the steel substrate.

Further, the ability of the amorphous aluminum phosphate to releaseinhibiting quantities of phosphate anion provides corrosion inhibitionat the sites of physical defects or damage in the film.

This discovery of the unique combination of passivation, wateradsorption, and nano-particle size and narrow/substantially uniformparticle size distribution allows the practical incorporation ofamorphous aluminum phosphate as a barrier enhancer in mid-coats andtopcoats not simply in primers. Conventional inhibitive pigments havevalue only in primers because they provide only a passivation mechanismof corrosion control. Amorphous aluminum phosphate and coatingcompositions comprising the same according to this invention protectsfrom corrosion by a dual mechanism: water adsorption enhancing barrierproperties and release of passivating anion.

Table 2 presents an example anticorrosion coating compositionformulation in the form of an acrylic latex primer composition preparedin the manner disclosed herein for purposes of reference.

TABLE 2 Example Acrylic Latex Based Anticorrosion Coating CompositionWater-based Primer Formula Water 111 lbs Pigment dispersant—SurfynolCT-131 23.4 lbs TiO2 color pigment 104.4 lbs Ammonium hydroxide 25% 1.6lbs Corrosion Inhibitive Pigment 50 lbs Extender Pigment—calciumcarbonate 183.7 lbs Disperse under high sheer 30 minutes Then mix in thefollowing Defoamer—Drewplus L-475 1.1 lbs Coalescent—I Eastman EB 49.2lbs Latex resin—Aquamac 740 506 lbs Coalescent II—Texanol ester alcohol9 lbs Coalescent III—Dowanol DPnB 14 lbs Dispersant/surfactant—SurfynolDF 210 2.4 lbs Additive 12.3 lbs Plasticizer—Santicizer 160 12.3 lbsFlash Rust Inhibitor—ammonium benzoate 3 lbs HASE Thickener—Acrysol TT615 4.06 lbs Defoamer 1.4 lbs

In this example, the pigment dispersant is Surfynol CT-131, thecorrosion inhibitive pigment is amorphous aluminum phosphate prepared bythe methods disclosed above and is provided in the form of powder, thedefoamer is Drewplus L-475, coalescent 1 is Eastman EB, coalescent 2 isDowanol DPnB, coalescent 3 is Texanol ester alcohol, thedispersant/surfactant is Surfynol DF 210, the plasticizer is Santicizer160, the flash rust inhibitor is ammonium benzoate salt, the HASEthickener is Acrysol TT 615. The loading of the amorphous aluminumphosphate in this formulation was approximately 4.6 percent by weightbased on the total weight of the composition.

As demonstrated above, embodiments of the invention provide a novelanticorrosion coating composition comprising amorphous aluminumphosphate. While the invention has been described with respect to alimited number of embodiments, the specific features of one embodimentshould not be attributed to other embodiments of the invention. Nosingle embodiment is representative of all aspects of the invention. Insome embodiments, the compositions or methods may include numerouscompounds or steps not mentioned herein.

For example, if desired, anticorrosion coating compositions can beprepared comprising one or more elements known to have anticorrosivevalue in addition to the amorphous aluminum phosphate, e.g., cationssuch as zinc, calcium, strontium, chromate, borate, barium, magnesium,molybdenum and combinations thereof. The addition of such otherelement(s) can operate to increase or complement the anticorrosiveeffect of the coating composition.

Additionally, while anticorrosion coating compositions as describedherein are engineered to include aluminum phosphate in an amorphousform, it is to be understood that anticorrosion compositions asdescribed herein can comprise aluminum phosphate in its knowncrystalline forms. For example, such crystalline aluminum phosphate canbe present in amounts that do not otherwise adversely impact or impairthe engineered anticorrosion mechanisms and/or properties of the coatingcomposition.

In other embodiments, the compositions or methods do not include, or aresubstantially free of, any compounds or steps not enumerated herein.Variations and modifications from the described embodiments exist. Themethod of making the coating compositions and/or amorphous aluminumphosphate is described as comprising a number of acts or steps. Thesesteps or acts may be practiced in any sequence or order unless otherwiseindicated. Finally, any number disclosed herein should be construed tomean approximate, regardless of whether the word “about” or“approximately” is used in describing the number. The appended claimsintend to cover all those modifications and variations as falling withinthe scope of the invention.

What is claimed:
 1. An aluminum phosphate prepared by the process of:combining an aluminum salt with phosphoric acid in the presence of waterto form a mixture; adding a sufficient amount of base material with themixture to form a sol comprising a dispersion of colloidal aluminumphosphate particles in liquid, wherein the colloidal particles aggregateupon adding further base material to form a gel structure, the gelcomprising a three-dimensional structure of linked-together colloidalaluminum phosphate particles; and heating the gel at a temperature ofless than about 300° C. to collapse the three-dimensional structure andform solid aluminum phosphate particles; wherein the particles aresubstantially spherical in shape and have a substantially uniform sizedistribution.
 2. The aluminum phosphate as recited in claim 1 whereinthe aluminum phosphate particles are aggregates of the colloidalparticles, wherein the colloidal particles have an average size of about1 to 100 nanometers.
 3. The aluminum phosphate as recited in claim 1wherein the aluminum phosphate particles consist of amorphous aluminumphosphate.
 4. The aluminum phosphate as recited in claim 1 wherein thealuminum salt is aluminum nitrate and the base material is ammoniumhydroxide.
 5. The aluminum phosphate as recited in claim 1, furthercomprising ammonium phosphate formed during the step of adding.
 6. Thealuminum phosphate as recited in claim 1 wherein the aluminum phosphateis free of alkali metal cations.
 7. The aluminum phosphate as recited inclaim 1 wherein the aluminum phosphate has a surface area of from 125m²/g to 150 m²/g.
 8. A chemical composition comprising the aluminumphosphate of claim 1 uniformly dispersed in a binding polymer.
 9. Thechemical composition as recited in claim 8 that provides a controlleddelivery of phosphate anion of about 100 to 1,500 ppm when applied to asubstrate and when contacted with water.
 10. The chemical composition asrecited in claim 8 further comprises a material including an elementselected from the group consisting of zinc, calcium, strontium,chromate, borate, barium, magnesium, molybdenum and combinationsthereof.
 11. The chemical composition as recited in claim 8 furthercomprising ammonium phosphate.
 12. The chemical composition as recitedin claim 8 wherein the aluminum phosphate has a total solubles contentof less than about 1,500 ppm.
 13. A method for making aluminum phosphatecomprising the steps of: combining an aluminum salt with phosphoric acidin an aqueous solution to form a mixture; and combining a sufficientamount of base material with the mixture to form a sol comprising adispersion of colloidal aluminum phosphate particles, wherein thecolloidal particles aggregate upon adding further base material to forma gel structure, the gel comprising a three-dimensional structure oflinked-together colloidal aluminum phosphate particles.
 14. The methodas recited in claim 13 wherein the sol comprises the dispersion ofcolloidal aluminum phosphate particles in a liquid, and wherein themethod further comprises treating the gel to collapse thethree-dimensional structure.
 15. The method as recited in claim 14wherein the step of treating comprises heating the gel to a temperatureof up to about 300° C. to remove the liquid and provide solid aluminumphosphate particles.
 16. The method as recited in claim 15 wherein thealuminum phosphate comprises amorphous aluminum phosphate.
 17. Themethod as recited in claim 15 wherein the aluminum phosphate consists ofamorphous aluminum phosphate.
 18. The method as recited in claim 15comprising combining the solid aluminum phosphate particles with abinding polymer such that the solid aluminum phosphate particles areuniformly dispersed therein to form a chemical composition.
 19. Themethod as recited in claim 18 wherein the chemical composition providesa controlled delivery of from 50 to 1,500 ppm phosphate anion when thechemical composition is applied to a substrate and in the presence ofmoisture.
 20. The method as recited in claim 18 wherein the bindingpolymer is selected from the group consisting of epoxy, acrylic latex,and acrylic copolymer latex.
 21. The method as recited in claim 18wherein the chemical composition additionally comprises a materialincluding an element selected from the group consisting of zinc,calcium, strontium, chromate, borate, barium, magnesium, molybdenum andcombinations thereof.
 22. The method as recited in claim 13 wherein thebase material is ammonium hydroxide, the aluminum salt is aluminumnitrate, and wherein ammonium nitrate is formed during one or both stepsof combining.
 23. The method as recited in claim 13 wherein thecolloidal particles have an average particle size of from about 1 to 100nanometers.
 24. The method as recited in claim 13 wherein the colloidalparticles are substantially spherical in shape and have a substantiallyuniform particle size distribution.
 25. A chemical compositioncomprising aluminum phosphate particles dispersed within a bindingpolymer, the chemical composition prepared by: combining aluminumnitrate with phosphoric acid in the presence of water to form a mixture;adding ammonium hydroxide to the mixture to form a sol comprising adispersion of colloidal aluminum phosphate particles in liquid; addingfurther ammonium hydroxide to the sol to cause the colloidal particlesto aggregate and form a gel having a three-dimensional structure oflinked aluminum phosphate particles enclosing the liquid; drying the gelto produce dried aluminum phosphate particles; and combining the driedaluminum phosphate particles with a binding polymer to form the chemicalcomposition.
 26. The chemical composition as recited in claim 25 furthercomprising ammonium phosphate.
 27. The chemical composition as recitedin claim 25 wherein the aluminum phosphate consists of amorphousaluminum phosphate.
 28. The chemical composition as recited in claim 25further comprising a material having an element selected from the groupconsisting of zinc, calcium, strontium, chromate, borate, barium,magnesium, molybdenum and combinations thereof.
 29. The chemicalcomposition as recited in claim 25 wherein the aluminum phosphate isalkali metal free.
 30. The chemical composition as recited in claim 25having a controlled phosphate anion release of between 50 to 1,500 ppmwhen applied to a substrate and contacted by water.
 31. The chemicalcomposition as recited in claim 25 wherein the aluminum phosphateparticles are substantially spherical in shape, and have an averagesurface area of from about 125 m²/g to 150 m²/g.
 32. The chemicalcomposition as recited in claim 25 wherein the aluminum phosphateparticles have uniform size distribution of from 10 to 100 nanometers.